Bone screw

ABSTRACT

A bone screw is provided including a tubular body and a head as separate parts. The tubular body has a first end, a second end, a tubular wall defining a cavity and a plurality of openings extending through the tubular wall into the cavity. The tubular body also includes a continuous exterior bone thread on an exterior tubular surface of the tubular wall. The continuous exterior bone thread extends for at least one full revolution about the tubular surface. The head defines an inner bore and includes an engagement structure to engage with a driver to advance the bone screw in the bone when a rotating force from the driver is applied to the engagement structure in a first direction, and a connection structure to connect to the tubular body at the first end. The head is connected to the tubular body by the connection structure in such a way that the head is locked against disconnection from the tubular body when a rotating force from a driver is applied to the engagement structure in a second direction opposite to the first direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of U.S. Provisional Application No. 61/293,433, filed Jan. 8, 2010, the entire contents of which are incorporated herein by reference. This application also claims priority to and the benefit of EP 10 150 373.8, filed in the European Patent Office on Jan. 8, 2010, the entire contents of which are incorporated herein by reference.

BACKGROUND

The invention relates to a bone screw. In particular, the invention relates to a bone screw that can be used as an anchor screw and a fusion screw that fuses with the surrounding bone material.

A bone screw that can be used as a fusion screw is known from US 2004/0015172 A1. This bone screw has a tubular thread section with a bone thread and with a plurality of recesses in its wall, a head, and a tip that can be connected to the tubular thread section. In use, the tubular portion can be filled with bone material or other growth promoting material and then the tip and/or the head are connected to the tubular portion. Usually the screw is inserted into a core hole in the bone, which is prepared in advance. After insertion of the screw into the bone, fusion of the screw with the surrounding bone material takes place. The screw can act as a traction element to connect shattered or split-off parts of bones together by means of the screw.

SUMMARY

It is the object of the invention to provide an improved bone screw of the aforementioned type, the position of which in the bone can be corrected after insertion and which can be easily removed later, if required.

The bone screw according to the invention is fillable with a substance to support fusion and is precisely positionable. When the bone screw is inserted into a core hole that has been prepared in advance, the bone thread at an exterior wall surface engages the bone and the screw is advanced by screwing it deeper into the bone by means of a screw driver. To adjust the position of the bone screw, it might be necessary to screw it back out to reposition the screw. This is facilitated, since the head and the tubular body of the bone screw are firmly connected without a risk of loosening or disconnection.

The bone screw can act as a bone anchor or can be used to connect broken elements of bones or as a support beam to strengthen weak bones.

In certain situations, it might be clinically necessary to remove an implanted bone screw at a later stage, when the bone screw may have already fused with the surrounding bone material. Since the head and the tubular body are firmly connected, it is possible to remove a bone screw that has already fused with the surrounding bone material.

Further features and advantages of the invention will become apparent from the description of embodiments of the invention by means of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective exploded view of a bone screw according to a first embodiment.

FIG. 2 shows a perspective view of the bone screw of FIG. 1 in an assembled state.

FIG. 3 shows an enlarged exploded side view of a bone screw according to the first embodiment, a tubular portion being shown only in part.

FIG. 4 shows a perspective exploded view of the bone screw of FIG. 3.

FIG. 5 shows a sectional view of the bone screw of FIG. 3 in an assembled state, the section being taken in a plane containing the screw axis.

FIG. 6 shows an sectional view of an enlarged portion of the bone screw according to FIG. 1 in the region of the tip, the section being taken in a plane containing the screw axis.

FIG. 7 shows an enlarged perspective view of the tip.

FIGS. 8 a to 8 d show steps of using the bone screw according to the first embodiment.

FIG. 9 shows a perspective exploded view of a bone screw according to a second embodiment.

FIG. 10 shows a perspective view of the bone screw of FIG. 9 in an assembled state.

FIG. 11 shows an enlarged portion of the bone screw of FIG. 9 in an exploded view.

FIG. 12 shows an enlarged sectional view of a portion of the tubular portion of the bone screw of FIG. 9.

FIG. 13 shows an enlarged sectional view of the connection of the tubular body with the head of the bone screw of FIG. 11.

FIG. 14 shows a modified example of the bone screw according to the previous embodiments in a side view.

DETAILED DESCRIPTION

The bone screw according to a first embodiment as shown in FIGS. 1 to 7 comprises a tubular body 1 with an open first end 2 and a second end 3 and a screw axis L. In the example shown, the tubular body is cylindrical. The tubular body has a tubular wall defining a cavity. On the exterior surface of the tubular wall, a so-called bone thread 4 is provided. In the embodiment shown, the bone thread is provided along the whole length of the tubular body. The bone thread 4 is configured to cut into the bone when the bone screw is screwed into the bone. Further, a plurality of openings 5 are located in the tubular wall, which extend entirely through the tubular wall into the cavity. The plurality of openings 5 are shown as diamond-shaped and are located between the crests of the bone thread 4. However, any other variations of the shapes and locations of the plurality of openings 5 are conceivable. The cavity provided by the tubular body 1 has a volume that is suitable for accommodating bone material. The wall thickness of the tubular body is preferably smaller than about 15% of the outer diameter of the tubular body.

As shown in FIG. 5, the tubular body 1 has in the region of its first end 2 an internal thread 6 provided on its interior wall surface. At the first end 2 a plurality of recesses 7 are provided in the wall of the tubular body, which extend in the axial direction from the first end 2 to a certain distance in direction of the second end 3. Seen in the radial direction, the recesses extend completely through the wall of the tubular body. In the embodiment shown, four triangular recesses 7 are provided at equidistant locations in the circumferential direction of the edge of the first end 2.

The bone screw further comprises a head 8 that is connectable to the first end 2. The head 8 is substantially cylindrical and has an outer diameter that is greater than the outer diameter of the tubular body 1. The head 8 has a first end 9 facing away from the tubular body 1 and a second end 10 facing the first end 2 of the tubular body. At its second end 10, the head 8 has a plurality of projections 11, the shape and location of which is such that the projections 11 engage the recesses 7 of the tubular body 1 so that a form-fit connection between the head 8 and the tubular body 1 is provided. In this embodiment, four equidistantly-located triangular projections extend from the second end 10 of the head 8. Instead of recesses at the tubular body and projections at the head, recesses can be present at the head and projections can be present at the tubular body, or the head and the tubular body can have both recesses and projections. The head 8 in this embodiment is cannulated. It comprises a coaxial bore 12 extending from the first end 9 to the second end 10 completely through the head.

At its first end 9 a recess 13 is provided, which is configured to engage with a screw driver used to screw the bone screw into the bone by rotating the driver in a first direction that is the screw-in direction. The recess 13 has an inner diameter that is larger than the inner diameter of the coaxial bore 12. The shape of the recess is, for example, a hexagon shape. However, any other shape that is suitable for engagement with a screw driver can be used. Such other shapes can be, for example, square shape or any other polygon shape or star shape, for example a Torx® shape. Between the recess 13 and the second end 10 of the head 8 there is a transition portion 14 that is, for example, a tapered portion that can act as an abutment for a securing screw with tapered head to be described below. However, the transition portion can have another shape adapted to the shape of the head of the securing screw or can be omitted. The second end 10 of the head 8 of the bone screw has preferably a flat surface in order to provide an abutment for the bone surface.

The bone screw also comprises a securing element 15 in the form of a screw, the screw thread of which cooperates with the internal thread 6 provided at the interior wall surface of the tubular body 1. The screw has a tapered head 16 abutting against the tapered transition portion 14 of the head. Further, a recess 17, for example, a polygon recess, is provided for engagement with a screw driver.

By means of the above described design, the head 8, which has the engagement structure for the screw driver to insert the screw into the bone, is connected by a form-fit connection to the tubular body, which prevents the head from being disconnected from the tubular body in the case that the screw driver is rotated in the reverse direction of the screw-in direction. Further, the connection between the head and the tubular body via the securing element is independent from the force acting onto the head when the screw is being screwed in.

For the securing element, other screw types or other devices such as a bayonet locking device can be used.

As shown in FIGS. 1, 6 and 7, the bone screw further has a separate tip 20 having a projection. The tip 20 in this embodiment is detachably connected to the tubular body 1. For this purpose, the tubular body 1 has adjacent to its second end 3 an internal thread 31, which can be engaged by an external thread 21 provided at the projection of the tip 20. In this embodiment, the tip 20 is cannulated. It has a coaxial bore 22 extending completely through the tip 20, which narrows towards the tip end opposite the projection. The tip 20 that is shown as an example also has a self-cutting structure 23, which allows the tip 20 to cut the bone when the bone screw is rotated so that it is not necessary to prepare a core hole in advance.

Other kinds of tips are conceivable. For example, the design of the tip can be such that it can be connected via a press-fit connection to the tubular body. Tips without self-cutting structures or without coaxial bores are also conceivable. Finally, it is also possible that the tip is integrally formed with the tubular body 1.

The coaxial bore 12 in the head and the coaxial bore 22 in the tip can serve as a guide structure for guiding a guide wire therethrough. They also can serve as a channel for introducing liquid bone cement or fluid drugs.

All parts of the bone screw are made of a body-compatible material such as a body-compatible metal, for example stainless steel or titanium; a body-compatible metal alloy, for example Nitinol; a body-compatible plastic material, for example PEEK; or combinations thereof.

In addition, the tubular body or the other parts of the bone screw can be coated with an in-growth promoting material or can be roughened to enhance in-growth of bone or vessels.

The steps of using the bone screw are shown in FIGS. 8 a to 8 d. In a first step shown in FIG. 8 a, the tip 20 is mounted onto the second end of the tubular body 1. Then, bone chips 100 are filled into the cavity provided by the tubular body 1. Then, as shown in FIG. 8 b, the head 8 and the securing screw 15 are mounted onto the first end of the tubular body 1. The head 8 is mounted such that the projections 11 at the second end 10 of the head engage the recesses 7 at the first end 2 of the tubular body. In this position, the securing screw 15 is introduced and tightened, so that the bone screw is closed, as shown in the side view of FIG. 8 c and the sectional view of FIG. 8 d.

The thus-prepared bone screw can be inserted into a core hole in the bone, which has been prepared in advance. The recess 13 is engaged with the screw driver (not shown) and the bone screw is advanced into the core hole by rotating the screwdriver in the screw-in direction. Slight corrections of the position of the bone screw in the core hole can be made by rotating the screwdriver in a reverse direction, so that the screw is screwed back out. Because of the shape-fit connection between the head and the tubular body, this is easily possible without the risk of loosening or disconnection of the head and the tubular body. After a certain time, fusion of the surrounding bone with the bone screw takes place.

In another embodiment of use, the coaxial bores 18 and 22 of the securing screw and the tip are used for guiding through a guide wire (not shown). In this case the guide wire, which is guided through the bone screw, is introduced through the skin of the patient and advanced through the tissue until it reaches the position where the bone screw is to be placed. The guide wire is inserted into the bone to the appropriate direction and depth. The bone screw is then guided along the guide wire extending therethrough until it reaches the surface of the bone and then screwed into the bone guided by the guide wire. This is in particular used in minimally invasive surgery (“MIS”).

A second embodiment is now described with reference to FIGS. 9 to 13. Identical parts are designated with the same reference numerals and the description thereof is not repeated. The tubular body 1′ of the second embodiment differs from the tubular body 1 of the first embodiment in that a recess in the form of a circumferential groove 60 is provided at the interior wall surface of the tubular body 1′ at a distance from the first end 2 and from the internal thread 6. The groove 60 serves for engagement with a projection provided at a head 80.

The head 80 has a first end 81 facing away from the tubular body 1′ and a second end 82 facing the tubular body F. The surface of the first end 81 can be, for example, lens-shaped. The second end 82 comprises a flat surface providing an abutment for the bone surface. At its second end 82, the head 80 has a cylindrical projection having a first portion 83 with an external thread that cooperates with the internal thread 6 provided at the interior wall surface of the tubular body 1′ adjacent the first end 2. Following the threaded portion 83 a substantially cylindrical portion with flexible wall sections 84 is provided. At the free end of each wall section 84, a projection 85 is provided, the shape of which is such that the projection 85 fits into the groove 60 of the tubular body 1′.

The axial length of the threaded projection 83 and the flexible wall sections 84 is such that, as shown in FIG. 13, when the head 80 is inserted into the tubular body 1′ and the threaded connection between the portion 83 and the internal thread 6 is tightened, the projection 85 engages the groove 60.

Further, the head 80 has a recess 86 at its first end for engagement with a screw driver. The recess 86 is shown to be star-shaped but can have any polygon shape. A coaxial bore 87 extends through the head 80, which has a portion within an internal thread 88 adjacent the recess 86 and which has in the region of the flexible wall sections 84 a section 89 with a smaller inner diameter that tapers in a portion 89 a towards the free end.

The securing element 50 according to the second embodiment is a set screw with a cylindrical projection 51 without a thread and with a taper 51 a at its free end. The set screw can be screwed into the coaxial bore of the head 80 when the head 80 is inserted into the tubular body, and tightened until the tapered section 89 a of the screw and the tapered section 51 a of the head engage each other. By means of this, the flexible wall portions 84 are slightly pressed outwards, so that the projections 85 engage the groove 60. When the projections 85 engage the groove 60, the head 80 is secured to the tubular body 1′ and cannot be loosened or disconnected. A coaxial bore 52 can be provided for guiding a guide wire therethrough.

Use of the bone screw according to the second embodiment is similar to the use of the bone screw according to the first embodiment. The description thereof will not be repeated.

FIG. 14 shows a bone screw according to a modified embodiment of the previous embodiments. Head 8 and tip 20 can be that of the first embodiment, the second embodiment or the third embodiment. The tubular body 1″′ has a first section 101 adjacent to the tip 20 comprising a bone thread 4, and a second section 102 adjacent to the head 8 with a smooth surface without a bone thread. The screw according to the modified embodiment can be used as a compression screw to press together two bone parts 201, 202. The bone screw is screwed into one bone part 202. In the other bone part 201 there is only a core hole, through which the first section 102 of the bone screw extends. By tightening the bone screw, the second end 10 of the head 8 abuts against the surface of the bone part 201 and presses the bone part 201 against the bone part 202. After a certain time, fusion of the bone parts 201, 202 with the bone screw and with each other takes place.

In a further modification, the second end 3 of the tubular body of all of the previous embodiments is free and the tip is omitted. In this case, the second end 3 can be provided with a plurality of cutting teeth that are configured to cut into the bone so that the cavity of the tubular body is automatically self-filled with cut bone material by screwing-in the bone screw into the bone.

In a further modification the outer diameter of the head may be equal to or even smaller than the outer diameter of the tubular body. This allows the bone screw to immerse fully into the bone.

In a further modification, the head and the tip are not cannulated. 

1. A bone screw comprising: a tubular body having a first end and a second end, wherein the tubular body has a tubular wall defining a cavity, a plurality of openings extending through the tubular wall into the cavity, and a continuous exterior bone thread on an exterior tubular surface of the tubular wall, wherein the continuous exterior bone thread extends for at least one full revolution about the tubular surface; a head defining an inner bore, the head comprising: an engagement structure to engage with a driver to advance the bone screw in the bone when a rotating force from the driver is applied to the engagement structure in a first direction, and a connection structure to connect to the tubular body at the first end; wherein the head and the tubular body are separate parts, and wherein the head is connectable to the tubular body by the connection structure in such a way that the head is locked against disconnection from the tubular body when a rotating force from a driver is applied to the engagement structure in a second direction opposite to the first direction.
 2. The bone screw of claim 1, wherein the head is connected to the tubular body by a form-fit connection.
 3. The bone screw of claim 1, wherein the head has at least one projection that engages in at least one recess of the tubular body.
 4. The bone screw of claim 3, wherein the at least one recess is provided at the edge of the first end.
 5. The bone screw of claim 3, wherein the at least one recess is provided at a distance from the first end.
 6. The bone screw of claim 1, wherein a securing element is provided for locking the head.
 7. The bone screw of claim 6, the securing element secures the head independently from the force acting onto the head by the driver.
 8. The bone screw of claim 6, wherein the securing element is an inner screw that is configured to be screwed into the inner bore of the head and connect the head to the tubular body.
 9. The bone screw of claim 1, wherein a tip is provided at the second end.
 10. The bone screw of claim 9, wherein the tip is a separate part from the tubular body.
 11. The bone screw of claim 9, wherein the tip is formed integrally with the tubular body.
 12. The bone screw of claim 1, wherein the wall thickness of the tubular body is smaller than about 15% of the outer diameter of the tubular body.
 13. The bone screw of claim 1, wherein the bone thread extends along the whole exterior surface of the tubular wall.
 14. The bone screw of claim 1, wherein a portion of the exterior surface is without bone thread.
 15. The bone screw of claim 14, wherein the portion of the exterior surface without bone thread is adjacent to the head.
 16. The bone screw according to claim 1, wherein the head has a first end facing away from the tubular body and a second end facing the tubular body and wherein the first end has a substantially flat portion providing an abutment.
 17. The bone screw according to claim 1, wherein the head comprises a guiding hole configured to guide a wire therethrough.
 18. The bone screw according to claim 1, wherein the tubular body is cylindrical.
 19. The bone screw according to claim 1, wherein the engagement portion is a recess that is coaxial to the screw axis and serves for engagement with the driver.
 20. The bone screw according to claim 9, wherein the head and the tip are cannulated for guiding a guide wire.
 21. The bone screw of claim 1, wherein the head has at least one recess that engages in at least one projection of the tubular body.
 22. The bone screw of claim 21 wherein the at least one projection is provided at the edge of the first end.
 23. The bone screw of claim 21, wherein the at least one projection is provided at a distance from the edge of the first end. 